In the existing metal wired mesh cages for keeping pets, a door capable of being opened and closed is disposed on one side of a cage, and the door is generally of a rotating type or a sliding type. Whether it is a rotating type or a sliding type, the door is generally locked via a bolt. During use, the bolt is capable of being moved left and right, or up and down, in manual operations. Such bolts are inconvenient to operate and are relatively laborious to operate especially when the metal wired mesh cage is rusted or insufficiently lubricated. In addition, as an independent part, the bolt is not integrated with the whole pet cage and may be separated from the bolt-insertion hole occasionally, causing unnecessary trouble to the users.